1. Field of the Invention
The present invention relates to a fuel absorbent having excellent durability and fuel absorbing/desorbing ability, and a process for making the fuel absorbent.
2. Description of Related Art
A large amount of fuel evaporates when it is supplied to an automobile fuel tank through a conventional fuel pump nozzle. Part of the fuel in the automobile tank and carburetor float chamber also evaporates, both while the automobile is running and when it is at rest.
In order to prevent evaporative leakage of fuel into the atmosphere, canisters, such as fuel evaporation loss control devices, filled with fuel absorbers are typically attached to, for example, automobile fuel tanks. Similar devices have also been employed to trap fuel evaporating or leaking from other types of fuel storage tanks. In such evaporation loss control devices, charcoal has been typically used as the fuel absorbent.
It has been proposed to use lipophilic polymer gels as fuel absorbents in Japanese Laid Open Patent Application Nos. 67222/1989 and 227861/1989. Such gels can be formed from polypropylene and styrene-butadiene copolymers. These conventional lipophilic gels absorb large amounts of liquid gasoline and its higher boiling point components, and then desorb them reversibly.
Conventional canisters employing such lipophilic gels are constructed so that liquid gasoline and gasoline components having 5 or more carbon atoms are absorbed by the lipophilic gels before they can contact charcoal because they degrade the working capacity of charcoal to absorb gasoline vapors, thus improving the working capacity, stability and regenerative properties of the canisters.
A conventional canister is shown in FIG. 1 (PRIOR ART). In order to obtain the fuel absorbent 25, fine polymer particles 22 can be applied to a thread-like or sheet-like base 9. The surface of the polymer particle 22 is covered with a dispersing agent which serves to bond each polymer particle 22 together to form the fuel absorbent 25. The polymer particle 22 is formed from an organic polymer compound comprising, for example, ethylene-propylene-diene copolymer, which has an excellent capacity to absorb the evaporated fuel. The polymer compound swells when absorbing the fuel, such as gasoline, because of a large affinity between the organic polymer compound and the evaporated fuel.
The fuel absorbent 25, however, is not firmly affixed to the base 9. After absorbing the fuel and becoming swollen, the fuel absorbent 25 is likely to fall off the base 9, which causes clogging in the canister, resulting in a reduced fuel absorbing/desorbing ability.
Another conventional canister is shown in FIG. 2 (PRIOR ART). A coating film 3, formed of urethane or silicone reaction product, can be coated on the surface of the fuel absorbent 25 which is affixed to the base 9. However, when the fuel absorbent 25 absorbs fuel above its absorption saturation ability, it falls off when it is subjected to vibration of the automobile.
Furthermore, friction occurs between bases 9, or between the base 9 and the container wall when the fuel absorbent 25 is subjected to the vibration of the automobile. Such friction will partially disintegrate the coating film 3 and the fuel absorbent 25 can fall off. As a result, the fuel absorbing/desorbing ability of the canister is deteriorated.